Fix Game and editor freeze when clicking on the game's title bar

[Hilderin]

• Fixes Game and editor freeze when clicking on the game's title bar #102724

Ok, that was a tricky problem!! After commetted most of the code in display_server_windows.cpp and embedded_process.cpp and still reproducing the issue, I found out the cause of the problem!! The problem was caused by the fact that the input queues of the editor and the game window were on the same thread. I still don't understand why the issue was visible only when trying to move the floating window, but detaching these input queues fixed the issue.

The reel fix is the addition of these lines in display_server_windows.cpp:

if (p_parent_hwnd) {
	DWORD mainThreadId = GetWindowThreadProcessId(owner_hwnd, nullptr);
	DWORD embeddedThreadId = GetCurrentThreadId();
	AttachThreadInput(embeddedThreadId, mainThreadId, FALSE);
}

The other modifications come from some side effects of the modification. Turns out, that detaching the input queue make the floating window a lot more responsive, causing to see some issues with the starting location passed to the embedded game when using the Floating Window.

[tetrapod00]

I tested locally and the fix works for me. I can't speak to the code quality.